Burkholderia Bacteria Produce Multiple Potentially Novel Molecules that Inhibit Carbapenem-Resistant Gram-Negative Bacterial Pathogens

Abstract

Antimicrobial resistance in Gram-negative pathogens represents a global threat to human health. This study determines the antimicrobial potential of a taxonomically and geographically diverse collection of 263 Burkholderia (sensu lato) isolates and applies natural product dereplication strategies to identify potentially novel molecules. Antimicrobial activity is almost exclusively present in Burkholderia sensu stricto bacteria and rarely observed in the novel genera Paraburkholderia, Caballeronia, Robbsia, Trinickia, and Mycetohabitans. Fourteen isolates show a unique spectrum of antimicrobial activity and inhibited carbapenem-resistant Gram-negative bacterial pathogens. Dereplication of the molecules present in crude spent agar extracts identifies 42 specialized metabolites, 19 of which represented potentially novel molecules. The known identified Burkholderia metabolites include toxoflavin, reumycin, pyrrolnitrin, enacyloxin, bactobolin, cepacidin, ditropolonyl sulfide, and antibiotics BN-227-F and SF 2420B, as well as the siderophores ornibactin, pyochelin, and cepabactin. Following semipreparative fractionation and activity testing, a total of five potentially novel molecules are detected in active fractions. Given the molecular formula and UV spectrum, two of those putative novel molecules are likely related to bactobolins, and another is likely related to enacyloxins. The results from this study confirm and extend the observation that Burkholderia bacteria present exciting opportunities for the discovery of potentially novel bioactive molecules.

Metabolic Footprints of Burkholderia Sensu Lato Rhizosphere Bacteria Active against Maize Fusarium Pathogens

“…The suppression effect was associated with the accumulation of ornibactin and pyochelin siderophores, in accordance with reports linking the antifungal behavior of some Burkholderia strains via iron sequestration through the synthesis of ornibactin [82,83], malleobactin and pyochelin [19,84]. Supporting evidence for this proposal was provided by a recent study that attributed the antimicrobial activity versus antibiotic resistant pathogens detected in Burkholderia sensu stricto bacteria to several metabolites, including the ornibactin and pyochelin siderophores [85]. Additional evidence showing that these metabolites were rarely present in strains classified within the Paraburkholderia, Trinickia and other genera was also in agreement with their lack of biocontrol capacity against phytopathogenic fungi, as reported in this and other studies.…”

Biosynthesis of Ditropolonyl Sulfide, an Antibacterial Compound Produced by Burkholderia cepacia Complex Strain R-12632

“…Semipreparative fractionation of crude extracts to detect ditropolonyl sulfide. Results from our earlier study (21) suggested that ditropolonyl sulfide was likely responsible for the observed antibacterial activity of strain R-12632. That study also showed that ditropolonyl sulfide could not be detected in crude agar extracts of strain R-12632 and that semipreparative fractionation combined with liquid chromatography-high-resolution mass spectrometry (LC-HRMS) was necessary to detect this compound.…”

“…Results from a previous study showed that Bcc strain R-12632 inhibited several important Gram-negative bacterial pathogens and suggested that ditropolonyl sulfide might be responsible for the observed activity (21). Ditropolonyl sulfide production was also a The genome of strain R-12632 was analyzed using antiSMASH v5.1.0 (57).…”

“…Through semipreparative fractionation and activity testing, three molecules were found in fractions that inhibited the Gram-negative bacterial pathogens A. baumannii LMG 10520 and Citrobacter freundii R-67508. Whereas pyrrolnitrin showed only weak activity, the fraction containing a mixture of ditropolonyl sulfide and a putative novel molecule with the molecular formula C 47 H 61 N 3 O 16 strongly inhibited growth of both pathogens (21). Although ditropolonyl sulfide was previously reported to inhibit Gram-negative bacterial pathogens (24), the pathway for its biosynthesis remains to be elucidated.…”

“…In a previous study (21), we examined the production of antimicrobial compounds by a diverse collection of Burkholderia bacteria and observed several Bcc strains that inhibited multiple Gram-negative bacterial pathogens, including A. baumannii and carbapenem-resistant strains of Klebsiella pneumoniae, Enterobacter spp., and Escherichia coli. Strain R-12632, an unclassified soil isolate from the maize rhizosphere (22) that has been referred to as "Other Bcc group I" and that is closely related to Burkholderia cenocepacia (23), produced a total of 17 specialized metabolites, including pyrrolnitrin, ornibactins (C4, C6, and C8), pyochelin, aerugine, aeruginoic acid, dihydroaeruginoic acid, and ditropolonyl sulfide, and seven potentially novel molecules (21). Through semipreparative fractionation and activity testing, three molecules were found in fractions that inhibited the Gram-negative bacterial pathogens A. baumannii LMG 10520 and Citrobacter freundii R-67508.…”